The present invention is related to logic circuits and, more particularly, to an Emitter-Coupled-Logic (ECL) circuit for providing differential outputs designed for bus driving applications.
Tri-state ECL bus drive integrated circuits are well known in the art. For instance, the MC10H123, Bus Driver, manufactured by Motorola, Inc., is such a circuit. These prior art bus drivers provide single-ended outputs consisting of Nor gates designed for bus driving applications as is well understood. Generally, the output of the bus driver is taken through an emitter-follower stage which, when disabled, goes low to produce an high impedance to the bus in the tri-level state.
At present, there is no known differential ECL bus driver integrated circuit that provides differential output logic signals for driving a bus in response to receiving differential input logic signals. It is desirable to provide differential outputs in order to drive a pair of bus lines differentially while not increasing additional time delays due to additional gate requirements. In addition, it is also desirable to maintain the necessary current drain to a minimum during the tri-state off condition when the differential outputs are in the high impedance state.
Hence, there is a need for an integrated ECL bus driver circuit for providing differential output logic states while minimizing gate time delays and current drain requirements.